1. Field of the Invention
The present invention relates to a pole plate assembly for a stator of a motor. In particular, the present invention relates to a pole plate assembly that has plural stacked pole plates having an increased overall thickness to avoid leakage of magnetic flux and to increase the rotational output torque. In addition, the number of pole faces is arranged in the most effective manner and the overall thickness of the respective pole face is decreased to reduce the radial dimension of the stator.
2. Description of the Related Art
FIG. 7 of the drawings illustrates a conventional stator of a motor. The stator comprises a bobbin 700, two pole plates 710, and an axle tube 720. Each pole plate 710 has two pole ends 711 each having a pole face 712 extending along a plane perpendicular to a generally plane of the respective pole plate 710. The axle tube 720 extends through the pole plates 710 and the bobbin 700 to thereby form a stator having four poles. When electric current is passed through the winding of the stator, the magnetic flux (magnetic lines) created by the winding is guided by the axle tube 720 and to pass through the pole plates 710 to each of the pole faces 712, thereby driving a permanent magnet on a rotor with the magnetic field created on the respective pole face 712. In physical properties, the amount of the magnetization or the magnetic dipole moment of the respective pole plate 710 is constant such that each pole plate 710 is magnetized by the axle tube 720 to a fixed extent. Therefore, the output torque of the stator to the rotor is not substantially increased and the rotational efficiency of the motor is reduced if the number of the pole faces 712 is increased for each pole plate 710. In brief, it is improper to arrange too many pole faces 712 on the respective pole plate 710. On the other hand, a single pole plate 710 cannot assure reliable guide of the magnetic field intensity in the axle tube 720 to the pole plate 710 without leakage of the magnetic flux. Thus, it is theoretically necessary to increase the number of pole plates in order to increase the guide effect of the magnetic flux on the axle tube 720. On the other hand, one must consider the total number of the pole plates while selecting the number of the pole faces on a pole plate so as to determine the most efficient number of the pole faces. For example, when manufacturing a four-pole motor with four pole plates, the most efficient number of the pole face is one (1) for each pole plate, and when manufacturing an eight-pole motor with four pole plates, the most efficient number of the pole faces is two (2).
FIG. 8 shows another conventional stator of a motor. The stator comprises a bobbin 800, two pole plates 810, and an axle tube 820. Each pole plate 810 includes four pole ends 811 and four pole faces 812 to thereby form a stator having eight poles. Compared with the stator shown in FIG. 7, even the number of the pole ends and the number of the pole faces for the respective pole plate are both increased, it was found that the output torque for driving the motor rotor was not increased significantly, as the sectional thickness of the respective pole plate was not increased at the same time.
A first object of the present invention is to provide a pole plate assembly for a stator of a motor, wherein the number of the pole plates of the pole plate assembly is increased to increase the total magnetic flux guided through the pole plates, thereby increasing the output torque for driving the rotor.
A second object of the present invention is to provide a pole plate assembly for a stator of a motor, wherein the number of each pole plate of the stator plate assembly is selected to be the most efficient to thereby reduce the overall thickness of the respective pole face. The radial dimension of the motor stator is reduced accordingly.
A stator in accordance with the present invention comprises a bobbin, plural pole plates, and an axle tube. A half of the plural pole plates is mounted on top of the bobbin and the other half of the plural pole plates is mounted to a bottom of the bobbin. The axle tube is extended through the pole plates and the bobbin to form a stator having four or eight poles. The magnetization is increased and the magnetic flux leakage is reduced by means of the increased overall thickness of the pole plates. The effective guided magnetic flux to the respective pole plate is gained. In addition, the radial dimension of the stator is reduced, as each pole plate is provided with the most efficient number of pole face(s) and the overall thickness of the respective pole face is reduced.